<?php if($id != ''):?>
  <div id="test_box">
    <?php echo $form['test_block']->renderError() ?>
    <?php echo $form['test_block'] ?>
  </div>
  <div id="test2_box">
  </div>
<script type="text/javascript">
    $('#Teststart_test_block').change(function() {
            value_subj = $('#Teststart_test_block').attr('value');
            $.ajax({
            data: ({block_id : value_subj }),
            url: "<?php echo url_for('@testbox2')?>",
            success: function(data) {
                $('div#test2_box').html(data);
          }});
    });
</script>
<?php endif;?>